buy a breeder net that sticks to the glass. put some of the tangs favorite food in there and when he swims in, turn it upright so he cant swim out.I'm in the same boat (120 gal). And made a decision to get rid of my favorite lavender tang.
Now, the question, how do you catch it ? rock-work has plenty of hiding places.
I have 7 inch lavender tang just for u.I think my tank could handle him I am very good with keeping up on tank maintenance but you do raise a good point semi aggressive fish could turn to aggressive fish and mess with the smaller fish. I think i will pass I just really like the way trigger fish look I guess it's on to the next one. Maybe another tang
Thanks everyone